1. Field of the Invention
The present invention relates to puffer type circuit breakers, and in particular to such circuit breakers having a gaseous arc-extinguishing medium and which generate a blast of arc-extinguishing gas towards the contact area of the circuit breaker.
2. Prior Art
Puffer type circuit breakers have a pump means consisting of a piston and a cylinder in order to compress gas in a pump chamber upon opening of the circuit breaker, from which pump chamber a flow of arc-extinguishing gas is led towards the contact area. Usually the piston of the pump means is fixedly arranged, whereas the cylinder is fixed to the movable contact, which is connected to an operating device via axially displaceable pull rod. The rod passes through an opening in the piston, and sealing and bearing means are arranged between the piston and the rod. In order to refill the pump chamber with arc-extinguishing gas upon closing of the breaker, there is often arranged a check valve in the pump piston. This valve is normally provided with a spring which biasses the movable valve member towards the closed valve position. Upon closing of the breaker, there will arise a pressure difference between the pump chamber and the surroundings which acts against the spring force, whereby the valve opens, enabling new arc-extinguishing gas to flow into the pump chamber. Circuit breakers of this design are known, for example, from the ASEA pamphlet KT 20-109 E, FIG. 14, April l978.